Along with miniaturization of transistors, in a thin film such as an insulating film forming a sidewall spacer (SWS) or the like of a gate electrode, a decrease in a film-forming temperature, a high resistance to hydrogen fluoride (HF), and a decrease in a dielectric constant are necessary. Accordingly, as the insulating film, employing a silicon boron nitride film (SiBN film) obtained by adding boron (B) to a silicon nitride film (a SiN film) or a silicon borocarbonitride film (a SiBCN film) further including carbon (C) has been studied.
Since a high step coverage characteristic is necessary, the above-described insulating film is frequently formed by an alternate supply method in which a plurality of types of processing gases are alternately supplied. For example, a SiBCN film may be formed on a substrate by performing a cycle a predetermined number of times. The cycle includes sequential supply of processing gases to the substrate, using a silicon-containing gas as a silicon (Si) source, a boron-containing gas as a B source, a carbon-containing gas as a C source and a nitrogen-containing gas as a nitrogen (N) source. However, in the above method in which the Si source, the B source, the C source and N source are separately supplied, a time required for one cycle increases, which results in a decrease of productivity in a film-forming process.